如何计算Ruby数组中的重复项

Question

你如何计算ruby数组中的重复项？

例如,如果我的数组有三个a,我怎么能算这个

Answer 1

另一个版本的哈希,其中包含数组中每个元素的键和每个元素的计数值

a = [ 1, 2, 3, 3, 4, 3]
h = Hash.new(0)
a.each { | v | h.store(v, h[v]+1) }

# h = { 3=>3, 2=>1, 1=>1, 4=>1 } 

Answer 2

鉴于:

arr = [ 1, 2, 3, 2, 4, 5, 3]

我最喜欢的计算元素的方法是:

counts = arr.group_by{|i| i}.map{|k,v| [k, v.count] }

# => [[1, 1], [2, 2], [3, 2], [4, 1], [5, 1]]

如果您需要哈希而不是数组:

Hash[*counts.flatten]

# => {1=>1, 2=>2, 3=>2, 4=>1, 5=>1}

Answer 3

这将生成重复元素作为散列,其中包含每个重复项的出现次数.让代码说:

#!/usr/bin/env ruby

class Array
  # monkey-patched version
  def dup_hash
    inject(Hash.new(0)) { |h,e| h[e] += 1; h }.select { 
      |k,v| v > 1 }.inject({}) { |r, e| r[e.first] = e.last; r }
  end
end

# unmonkeey'd
def dup_hash(ary)
  ary.inject(Hash.new(0)) { |h,e| h[e] += 1; h }.select { 
    |_k,v| v > 1 }.inject({}) { |r, e| r[e.first] = e.last; r }
end

p dup_hash([1, 2, "a", "a", 4, "a", 2, 1])
# {"a"=>3, 1=>2, 2=>2}

p [1, 2, "Thanks", "You're welcome", "Thanks", 
  "You're welcome", "Thanks", "You're welcome"].dup_hash
# {"You're welcome"=>3, "Thanks"=>3}

Answer 4

简单.

arr = [2,3,4,3,2,67,2]
repeats = arr.length - arr.uniq.length
puts repeats

Answer 5

arr = %w( a b c d c b a )
# => ["a", "b", "c", "d", "c", "b", "a"]

arr.count('a')
# => 2

Answer 6

计算数组重复的另一种方法是:

arr= [2,2,3,3,2,4,2]

arr.group_by{|x| x}.map{|k,v| [k,v.count] }

结果是

[[2,4],[3,2],[4,1]]

Answer 7

要求1.8.7+ group_by

ary = %w{a b c d a e f g a h i b}
ary.group_by{|elem| elem}.select{|key,val| val.length > 1}.map{|key,val| key}
# => ["a", "b"]

使用1.9+可以略微简化,因为Hash #select会返回一个哈希值.

ary.group_by{|elem| elem}.select{|key,val| val.length > 1}.keys
# => ["a", "b"]